Zoom lens system

ABSTRACT

A very compact zoom lens system is provided which has a zoom ratio of 10×, a bright f-number of 1.4 and a wide angle of view of 59 degree or greater although having a fewer number of lens. The zoom lens system comprises from the object side to the image side: a fixed first lens unit having a negative power lens, a positive power lens and a positive power meniscus lens; a second lens unit having an aspherical surface, having a negative power lens, a negative power biconcave lens and a positive power lens and performing zooming by moving; a fixed third lens unit having an aspherical surface and having a positive power lens, a positive power lens and a negative power lens; and a fourth lens unit having an aspherical surface, having positive power and moves according to zooming and a movement of an object point. The image side surface of the most image side lens of the third lens unit is a concave surface having strong power to the image side. When the focal length at the wide-angle limit is fw, the angle of view at the wide-angle limit is ω, the focal length of the first lens unit is f1 and the focal length of the second lens unit is f2, the following condition is satisfied: 
     
         0.17&lt;(fw×tanω)/(f1×|f2|).sup.1/2 &lt;0.39.

This application is a 371 of PCT/JP97/01210, Apr. 8, 1997.

TECHNICAL FIELD

The present invention relates to a zoom lens system for use in asingle-plate video camera, etc., having a wide angle of view (59 degreeor greater) and a high zoom ratio (approximately 10×).

BACKGROUND ART

Size reduction of image pickup devices and size reduction of lenssystems is greatly demanded in today's video camera market. Moreover, itis an important factor that electronic still-video cameras which haveappeared in recent years with the spread of multimedia personalcomputers are inexpensive and small in size. On the contrary, for themanufacturers, it is necessary to reduce the cost in order to havecompetitive power in the market. In order to reduce lens systems incost, it is necessary to provide a construction of lens system which hasa minimum number of lens elements and is capable of maintainingperformance the same as or higher than that of conventional lens systemswhile having a minimum number of lens elements.

For these reasons, it has conventionally been a problem how a zoom lenssystem is provided to be is small in size and high in resolution but hasa fewer number of lens elements.

A conventional zoom lens system will be described.

FIG. 32 is a view showing the structure of a conventional zoom lenssystem for use in a video camera described, for example, in JapaneseLaid-open Patent Publication Number Hei 6-109975. The zoom lens systemshown in the figure comprises a first lens unit 321 serving as acondenser unit, a second lens unit 322 serving as a zooming unit, athird lens unit 323 serving as a condenser unit, a fourth lens unit 324serving as a focusing unit, an equivalent glass plate 325 correspondingto a crystal filter or a faceplate of an image pickup element, etc., andan image forming plane 326.

The first lens unit 321 fixed in relation to the image forming plane 326has imaging function, and the second lens unit 322 moved back and forthalong the optical axis varies the magnification thereby to vary thefocal length of the overall lens system. The third lens unit 323 whichis a stationary unit condenses light diverged by the second lens unit322, and the fourth lens unit 324 moved back and forth along the opticalaxis has focusing function. Moreover, the variation in position of theimage plane caused by the movement of the second lens unit 322 duringzooming is corrected by the movement of the fourth lens unit 324 so asto image in a fixed position, whereby the image plane is alwaysmaintained in a fixed position.

However, in the conventional zoom lens system as described above, whatis called f-number is 1.6 or higher although the number of lens elementsis ten and the zoom ratio is approximately 10×. Therefore, it cannotcope with the insufficient sensitivity which is a problem in reducing ofimage size. Moreover, although having a small number of lens elements,its overall length is comparatively large and it lacks compactness. Forthis reason, it is a problem that the conventional zoom lens systemcannot fulfill the harsh demand for zoom lens systems for video cameraswhich is to be smaller in size and has higher performance. Moreover, itis difficult for the conventional zoom lens design technique to producea zoom lens system which fulfills all of a large aperture, a highmagnification, a smaller size and a higher resolution.

DISCLOSURE OF INVENTION

The present invention is intended for solving the above-mentionedproblems and an object of the present invention is to provide a verycompact zoom lens system with an f-number of approximately 1.4 and azoom ratio of approximately 10× although having a simple lensarrangement including ten lens elements, by employing an optimum lensarrangement and an optimum aspherical configuration. Another object isto provide a small-size video camera and a small-size electronic stillcamera, etc. using the zoom lens system.

A zoom lens system of the present invention is that, in a certainstructure having a first lens unit to a fourth lens unit, the respectivelens units are structured as follows.

The first lens unit comprises, from the object side, a lens elementhaving negative refractive power, a lens element having positiverefractive power and a meniscus lens element having positive refractivepower and convex to the object side.

The second lens unit comprises, from the object side, a lens elementhaving negative refractive power, a biconcave lens element havingnegative refractive power and a lens element convex to object sidesurface connected to the biconcave lens element and having positiverefractive power, and at least one of the surfaces of the lens elementsis aspherical.

The third lens unit comprises, from the object side, a lens elementhaving positive refractive power, a lens element having positiverefractive power and a lens element having negative refractive power,and at least one of the surfaces of the lens elements is aspherical.

The fourth lens unit comprises at least one lens element, and at leastone of the surfaces of the lens element is aspherical. Moreover, whenthe focal length at the wide-angle limit is fw, the half view angle atthe wide-angle limit is ω, the focal length of the first lens unit is f1and the focal length of the second lens unit is f2, the following issatisfied:

    0.17<(fw×tanω)/(f1×|f2|).sup.1/2 <0.39

By the interaction among the above-described lens units, a compact zoomlens system in which aberration is sufficiently corrected, the angle ofview at the wide-angle limit is approximately 59 degree and the zoomratio is approximately 10× is obtained with a simple structure.

A zoom lens system of the present invention comprises, from the side ofan object which is a subject: a first lens unit having positiverefractive power and fixed in relation to an image plane; a second lensunit having negative refractive power and performing zooming by movingalong the optical axis; a third lens unit having positive refractivepower which is fixed in relation to the image plane and performscondensing; and a fourth lens unit having positive refractive powerwhich moves along the optical axis so that the image plane variedaccording to the movement of the second lens unit and a movement of theobject which is the subject is maintained in a certain position inrelation to a reference plane,

wherein the first lens unit comprises, from the object side: a firstlens element of the first lens unit having negative refractive power; asecond lens element of the first lens unit having positive refractivepower; and a meniscus lens element having positive refractive power andconvex to the object side;

wherein the second lens unit comprises, from the object side: a firstlens element of the second lens unit having negative refractive power; abiconcave lens element having negative refractive power; and a secondlens element of the second lens unit having positive refractive powerwhich is convex to object side surface connected to the biconcave lenselement, at least one of the surfaces of the lens elements isaspherical,

wherein the third lens unit comprises, from the object side: a firstlens element of the third lens unit having positive refractive power; asecond lens element of the third lens unit having positive refractivepower; and a third lens element of the third lens unit having negativerefractive power, at least one of the surfaces of the lens elements isaspherical,

wherein the fourth lens unit comprises at least one lens element of thefourth lens unit, at least one of the surfaces of the lens element ofthe fourth lens unit is aspherical, and

wherein, when the focal length of the zoom lens system at the wide-anglelimit is fw, the half view angle at the wide-angle limit is ω, the focallength of the first lens unit is f1 and the focal length of the secondlens unit is f2, the following is satisfied:

    0.17<(fw×tanω)/(f1×|f2|).sup.1/2 <0.39 (1)

The conditional expression (1) is an expression regarding the back focallength and the angle of view, and when the value of(fw×tanω)/(f1×|f2|)^(1/2) is lower than the lower limit of theconditional expression (1), a sufficient back focal length is notobtained although the angle of view increases. On the contrary, when thevalue of (fw×tanω)/(f1×|f2|)^(1/2) exceeds the upper limit of theconditional expression (1), a wide angle of view is not obtainedalthough a sufficient back focal length is obtained. That is, by settingthe value so that the conditional expression (1) is satisfied, asufficient back focal length and a wide angle of view (59 degree orgreater) are obtained.

In the above-mentioned arrangement, when p3c is the refractive power ofthe image side surface of the third lens element of the third lens unitand fw is the focal length of the entire zoom lens system at thewide-angle limit, the following is preferably satisfied:

    0.40<fw×|p3c|<1.04                 (2)

Here, the refractive power of a surface is a value obtained by (n2-n1)/rwhere the refractive power of a medium on the incident side of thesurface is n1, the refractive power of a medium on the exit side of thesurface is n2 and the radius of curvature of the surface is r.

The conditional expression (2) is an expression regarding the f-numberand the back focal length and is closely related to the compactness ofthe zoom lens system. When the value of fw×|p3c| is lower than the lowerlimit of the conditional expression (2), a sufficient back focal lengthis not obtained although a low f-number is secured. On the contrary,when the value of fw×|p3c| exceeds the upper limit of the conditionalexpression (2), the back focal length increases to secure a sufficientf-number, so that the compactness of the zoom lens system is impaired.That is, by setting the value so that the conditional expression (2) issatisfied, a zoom lens system is obtained which is very compact in sizewhile securing sufficient f-number and back focal length.

Preferably, in the third lens unit, the first lens element of the thirdlens unit is a biconvex lens; the second lens element of the third lensunit is disposed so as to be convex to the object side; the third lenselement of the third lens unit has its object side surface connected tothe second lens element of the third lens unit and has its image sidesurface formed to be concave; and the overall refractive power of thesecond lens element of the third lens unit and the third lens element ofthe third lens unit connected each other is negative.

In the third lens unit, it may be so that the first lens element of thethird lens unit is a biconvex lens; the second lens element of the thirdlens unit is disposed so as to be convex to the object side; and thethird lens element of the third lens unit has its image side surfaceformed to concave, and these lens elements are disposed with spacestherebetween.

Preferably, in the above-mentioned arrangements, when fw is the focallength at the wide-angle limit and fi (i=1, 2, 3, 4) is the focal lengthof an ith lens unit, the following conditional expressions (3) to (6)are satisfied:

    0.14<fw/f1<0.31                                            (3)

    0.76<fw/|f2|<1.57                        (4)

    0.30<fw/f3<0.59                                            (5)

    0.26<fw/f4<0.55                                            (6)

The conditional expressions (3) to (6) are conditional expressions whichdefine the refractive power of the respective lens units, and bysatisfying these conditional expressions, a strong refractive power isobtained which realizes the compactness of the zoom lens system.

Moreover, when fw is the focal length at the wide-angle limit, fi (i=1,2, 3, 4) is the focal length of an ith lens unit, ω is the half viewangle at the wide-angle limit and p3c is the refractive power of theimage side surface of the third lens element of the third lens unit, itis more desirable that the following conditional expressions (7) to (12)be satisfied:

    0.255<(fw×tanω)/(f1×|f2|).sup.1/2 <0.301                                                    (7)

    0.643<fw×|p3c|<0.799               (8)

    0.212<fw/f1<0.232                                          (9)

    1.081<fw/|f2|<1.205                      (10)

    0.434<fw/f3<0.453                                          (11)

    0.376<fw/f4<0.421                                          (12)

Preferably, in the first lens element of the third lens unit, the secondlens element of the third lens unit and the third lens element of thethird lens unit, when the focal length of the first lens element of thethird lens unit is f31 and the composite focal length of the second lenselement of the third lens unit and the third lens element of the thirdlens unit is f323, the third lens unit satisfies the following:

    0.34<f31/|f323|<1.05                     (13)

The conditional expression (13) is a conditional expression regardingthe back focal length and the f-number, and when the value of f31/|f323|is lower than the lower limit of the conditional expression (13), thediameter of the third lens unit 3 increases to secure a sufficientf-number, and in addition, since the back focal length increases, acompact zoom lens system cannot be realized. Moreover, when the value off31/|f323| exceeds the upper limit of the conditional expression (13), asufficient back focal length is not obtained although a sufficientf-number is secured. That is, by structuring so that the conditionalexpression (13) is satisfied, a sufficient back focal length is obtainedin spite of the compact structure.

When the local radius of curvature at an aperture 10% of the effectiveaperture of the object side aspherical surface of the first lens elementof the third lens unit is r311, the local radius of curvature at anaperture 90% of the effective aperture of the object side asphericalsurface of the first lens element of the third lens unit is r319, thelocal radius of curvature at an aperture 10% of the effective apertureof the image side aspherical surface of the first lens element of thethird lens unit is r321, the local radius of curvature at an aperture90% of the effective aperture of the image side aspherical surface ofthe first lens element of the third lens unit is r329, the radius ofcurvature at an aperture 10% of the effective aperture of the objectside aspherical surface of the biconcave lens element of the second lensunit is r211, the local radius of curvature at an aperture 90% of theeffective aperture of the object side aspherical surface of thebiconcave lens element of the second lens unit is r219, and the lenselement of the fourth lens unit has an aspherical surface on its objectside surface, the local radius of curvature at an aperture 10% of theeffective aperture of the lens element is r411 and the local radius ofcurvature at an aperture 90% of the effective aperture of the lenselement is r419, or the lens element of the fourth lens unit has anaspherical surface on its image side surface, the local radius ofcurvature at an aperture 10% of the effective aperture of the lenselement is r421 and the local radius of curvature at an aperture 90% ofthe effective aperture of the lens element is r429, it is desirable thatthe following conditional expressions (14) to (18) be satisfied:

    0.29<r311/r319<1.00                                        (14)

    0.14<r321/r329<0.72                                        (15)

    0.74<r211/r219<1.52                                        (16)

and

    0.34<r411/r419<1.03                                        (17)

or

    0.64<r421/r429<1.91                                        (18)

The local radius of curvature is a value obtained by executing analgebraic calculation based on an aspherical coefficient calculated fromthe amount of sag of the surface configuration (amount of displacementfrom a reference surface).

The conditional expressions (14) to (18) are conditional expressionswhich define the aspherical amount and are conditions for obtaining asufficient aberration correction capability to realize a high resolutionof the zoom lens system.

Moreover, when the local radius of curvature at an aperture 10% of theeffective aperture of the object side aspherical surface of the firstlens element of the third lens unit is r311, the local radius ofcurvature at an aperture 90% of the effective aperture of the objectside aspherical surface of the first lens element of the third lens unitis r319, the local radius of curvature at an aperture 10% of theeffective aperture of the image side aspherical surface of the firstlens element of the third lens unit is r321, the local radius ofcurvature at an aperture 90% of the effective aperture of the image sideaspherical surface of the first lens element of the third lens unit isr329, the radius of curvature at an aperture 10% of the effectiveaperture of the object side aspherical surface of the biconcave lenselement of the second lens unit is r211, the local radius of curvatureat an aperture 90% of the effective aperture of the object sideaspherical surface of the biconcave lens element of the second lens unitis r219, and the lens element of the fourth lens unit has an asphericalsurface on its object side surface, the local radius of curvature at anaperture 10% of the effective aperture of the lens element is r411 andthe local radius of curvature at an aperture 90% of the effectiveaperture of the lens element is r419, or the lens element of the fourthlens unit has an aspherical surface on its image side surface, the localradius of curvature at an aperture 10% of the effective aperture of thelens element is r421 and the local radius of curvature at an aperture90% of the effective aperture of the lens element is r429, it is moredesirable that the following conditions (20) to (25) be satisfied:

    0.492<f31/|f323|<0.827                   (20)

    0.412<r311/r319<0.767                                      (21)

    0.193<r321/r329<0.551                                      (22)

    1.059<r211/r219<1.170                                      (23)

and

    0.490<r411/r419<0.787                                      (24)

or

    0.915<r421/r429<1.470                                      (25)

(Please note that (19) is skipped.)

A video camera or an electronic still camera of the present inventionuses a zoom lens system having any of the above-described structures.

Novel features of the invention are particularly described in theappended claims, and structures and contents of the present invention,together with other objects and features, will be more clearlyunderstood from the following detailed description given with referenceto the drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing the structure of a zoom lens system accordingto a first embodiment of the present invention.

FIG. 2 is a view showing the structure of a zoom lens system accordingto a second embodiment of the present invention.

FIG. 3 is a view showing aberration capability at a wide-angle limit ofa zoom lens system according to a first concrete numerical example ofthe first embodiment.

FIG. 4 is a view showing aberration at a standard position of the zoomlens system.

FIG. 5 is a view showing aberration at a telephoto limit of the zoomlens system.

FIG. 6 is a view showing aberration capability at the wide-angle limitof a zoom lens system according to a second concrete numerical exampleof the first embodiment.

FIG. 7 is a view showing aberration at the standard position of the zoomlens system.

FIG. 8 is a view showing aberration at the telephoto limit of the zoomlens system.

FIG. 9 is a view showing aberration capability at the wide-angle limitof a zoom lens system according to a third concrete numerical example ofthe first embodiment.

FIG. 10 is a view showing aberration at the standard position of thezoom lens system.

FIG. 11 is a view showing aberration at the telephoto limit of the zoomlens system.

FIG. 12 is a view showing aberration capability at the wide-angle limitof a zoom lens system according to a fourth concrete numerical exampleof the first embodiment.

FIG. 13 is a view showing aberration at the standard position of thezoom lens system.

FIG. 14 is a view showing aberration at the telephoto limit of the zoomlens system.

FIG. 15 is a view showing aberration capability at the wide-angle limitof a zoom lens system according to a fifth concrete numerical example ofthe first embodiment.

FIG. 16 is a view showing aberration at the standard position of thezoom lens system.

FIG. 17 is a view showing aberration at the telephoto limit of the zoomlens system.

FIG. 18 is a view showing aberration capability at the wide-angle limitof a zoom lens system according to a sixth concrete numerical example ofthe first embodiment.

FIG. 19 is a view showing aberration at the standard position of thezoom lens system.

FIG. 20 is a view showing aberration at the telephoto limit of the zoomlens system.

FIG. 21 is a view showing aberration capability at the wide-angle limitof a zoom lens system according to a seventh concrete numerical exampleof the first embodiment.

FIG. 22 is a view showing aberration at the standard position of thezoom lens system.

FIG. 23 is a view showing aberration at the telephoto limit of the zoomlens system.

FIG. 24 is a view showing aberration capability at the wide-angle limitof a zoom lens system according to an eighth concrete numerical exampleof the first embodiment.

FIG. 25 is a view showing aberration at the standard position of thezoom lens system.

FIG. 26 is a view showing aberration at the telephoto limit of the zoomlens system.

FIG. 27 is a view showing aberration capability at the wide-angle limitof a zoom lens system according to a concrete numerical example of thesecond embodiment.

FIG. 28 is a view showing aberration at the standard position of thezoom lens system.

FIG. 29 is a view showing aberration at the telephoto limit of the zoomlens system.

FIG. 30 is a view showing the structure of a video camera using a zoomlens system according to the first embodiment or the second embodiment.

FIG. 31 is a view showing the structure of an electronic still camerausing a zoom lens system according to the first embodiment or the secondembodiment.

FIG. 32 is a view showing the structure of a conventional zoom lenssystem.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the zoom lens system of the presentinvention will be described in detail with reference to the drawings.

<<First Embodiment>>

FIG. 1 is a view showing the structure of a zoom lens system accordingto a first embodiment. The zoom lens system shown in FIG. 1 comprises,from the object side (the left side of the figure): a first lens unit 1having positive refractive power and fixed in relation to an image plane6; a second lens unit 2 having negative refractive power and performingzooming by moving back and forth along the optical axis; a third lensunit 3 having positive refractive power which is fixed in relation tothe image plane and performs condensing; and a fourth lens unit 4 havingpositive refractive power which moves along the optical axis so that theimage plane varying responding to the movement of the second lens unit 2and a movement of the object which is the subject is maintained in acertain position in relation to a reference plane. Moreover, between thefourth lens unit 4 and the image plane 6, a flat plate 5 is placed whichis equivalent to an optical low-pass filter or a faceplate of an imagepickup device, etc.

The first lens unit 1 comprises, from the object side: a lens element 1ahaving negative refractive power; a lens element 1b having positiverefractive power; and a meniscus lens element 1c convex to the objectside and having positive refractive power.

The second lens unit 2 comprises, from the object side: a lens element2a having negative refractive power; a biconcave lens element 2b havingnegative refractive power; and a lens element 2c convex to object sidesurface connect to the biconcave lens element 2b and having positiverefractive power. At least one of the respective surfaces of the lenselements of the second lens unit 2 is aspherical.

The third lens unit 3 comprises, from the object side: a biconvex lenselement 3a having positive refractive power and whose both side surfacesare aspherical; a lens element 3b convex to the object side and havingpositive refractive power; and a lens element 3c having negativerefractive power. The lens element 3b having positive refractive powerand the lens element 3c having negative refractive power are connectedeach other. The positive refractive power of the biconvex lens element3a is set comparatively stronger than the refractive power correspondingto the composite focal length of the lens elements 3b and 3c connectedeach other. With this setting, a sufficient back focal length isobtained and aberration is sufficiently corrected although the lenssystem is very compact in size.

The fourth lens unit 4 comprises one biconvex lens element 4a and atleast one of the surfaces of the lens element 4a is aspherical.

In FIG. 1, Si (i=1, - - - , 19) represents the surface number of therespective lens elements, ri (i=1, - - - , 17) represents the radius ofcurvature of the respective lens elements, dk (k=1, - - - , 18)represents the thickness of the lens elements or the air spaces betweenthe lens elements. The connecting surfaces of two lens elements and theradii of curvature thereof are designated by the same numbers.

When the focal length at the wide-angle limit is fw, the focal length ofthe first lens unit 1 is f1, the focal length of the second lens unit 2is f2 and the angle of view at the wide-angle limit is ω, the followingis satisfied:

    0.255<(fw×tanω)/(f1×|f2|).sup.1/2 <0.301                                                    (7)

The conditional expression (7) is a expression regarding the back focallength and the angle of view, and when the value of(fw×tanω)/(f1×|f2|)^(1/2) is lower than the lower limit of theconditional expression (7), a sufficient back focal length is notobtained although the angle of view increases. On the contrary, when thevalue of (fw×tanω)/(f1×|f2|)^(1/2) exceeds the upper limit of theconditional expression (7), a wide angle of view is not obtainedalthough a sufficient back focal length is obtained.

<<Second Embodiment>>

FIG. 2 is a view showing the structure of a zoom lens system accordingto a second embodiment. The zoom lens system shown in FIG. 2 comprises,from the object side (the left side of the figure): a first lens unit 1having positive refractive power and fixed in relation to an image plane6; a second lens unit 2 having negative refractive power and performingzooming by moving back and forth along the optical axis; a third lensunit 3 having positive refractive power which is fixed in relation tothe image plane and performing condensing; and a fourth lens unit 4having positive refractive power which moves along the optical axis sothat the image plane varying responding to the movement of the secondlens unit 2 and a movement of the object which is the subject ismaintained in a certain position in relation to a reference plane.Moreover, between the fourth lens unit 4 and the image plane 6, a flatplate 5 is placed which is equivalent to an optical low-pass filter or afaceplate of an image pickup device, etc.

The first lens unit 1 comprises, from the object side: a lens element 1ahaving negative refractive power; a lens element 1b having positiverefractive power; and a meniscus lens element 1c convex to the objectside which has positive refractive power.

The second lens unit 2 comprises, from the object side: a lens element2a having negative refractive power; a biconcave lens element 2b havingnegative refractive power; and a lens element 2c convex to object sidesurface connected to the biconcave lens element 2b and having positiverefractive power. At least one of the surfaces of the lens elements ofthe second lens unit 2 is aspherical.

The third lens unit 3 comprises, from the object side: a biconvex lenselement 3a having positive refractive power and whose both side surfacesare aspherical; a lens element 3b having positive refractive power whichis convex to the object side; and a lens element 3c having negativerefractive power. The lens element 3b having positive refractive powerand the lens element 3c having negative refractive power are disposedwith a slight air space therebetween unlike the first embodiment inwhich they are connected. The refractive power of the biconvex lenselement 3a is set comparatively stronger than the composite refractivepower of the lens elements 3b and 3c. With this setting, a sufficientback focal length is obtained and aberration is sufficiently correctedalthough the lens system is very compact in size.

The fourth lens unit 4 comprises one biconvex lens element 4a and atleast one of the surfaces of the lens element 4a is aspherical.

In FIG. 2, Si (i=1, - - - , 20) represents the surface number of therespective lens elements, ri (i=1, - - - , 18) represents the radius ofcurvature of the respective lens elements, dk (k=1, - - - , 19)represents the thickness of the lens elements or the air spaces betweenthe lens elements. The connecting surfaces of two lens elements and theradii of curvature thereof are designated by the same numbers.

When the focal length at the wide-angle limit is fw, the focal length ofthe first lens unit is f1, the focal length of the second lens unit isf2 and the angle of view at the wide-angle limit is ω, the followingrelationship is satisfied:

    0.255<(fw×tanω)/(f1×|f2|).sup.1/2 <0.301                                                    (7)

The conditional expression (7) is an expression regarding the back focallength and the angle of view, and when the value of(fw×tanω)/(f1×|f2|)^(1/2) is lower than the lower limit of theconditional expression (7), a sufficient back focal length is notobtained although the angle of view increases. On the contrary, when thevalue of (fw×tanω)/(f1×|f2|)^(1/2) exceeds the upper limit of theconditional expression (7), a wide angle of view is not obtainedalthough a sufficient back focal length is obtained.

<<Supplemental Remarks Common to the First and Second Embodiments>>

The above-mentioned first and second embodiments both satisfy thefollowing condition:

    0.643<fw×|p3c|<0.799               (8)

The conditional expression (8) is an expression regarding the f-numberand the back focal length and is closely related to the compactness ofthe zoom lens system. When the value of fw×|p3c| is lower than the lowerlimit of the conditional expression (8), a sufficient back focal lengthis not obtained although a low f-number is secured. On the contrary,when the value of fw×|p3c| exceeds the upper limit of the conditionalexpression (8), the back focal length increases in order to secure asufficient f-number, so that the compactness is impaired. However, inthese embodiments, since fw×|p3c| is set so as to satisfy theconditional expression (8), a zoom lens system is obtained which is verycompact in size while securing sufficient f-number and back focallength.

The focal lengths fi (i=1, - - - , 4) of the first to fourth lens unitsare set by the following conditions when the focal length at thewide-angle limit is fw:

    0.212<fw/f1<0.232                                          (9)

    1.081<fw/|f2|<1.205                      (10)

    0.434<fw/f3<0.453                                          (11)

    0.376<fw/f4<0.421                                          (12)

The conditional expressions (9) to (12) are conditional expressionswhich define the refractive power of the respective lens units andprovide a strong refractive power which achieves the compactness of thezoom lens system.

In the conditional expression (9) regarding the refractive power of thefirst lens unit 1, when the value of fw/f1 is lower than the lower limitof the conditional expression (9), the refractive power of the firstlens unit 1 is too strong. For this reason, it is difficult to correctspherical aberration on the longer focal length side and off-axial coma.On the contrary, when the value of fw/f1 exceeds the upper limit of theconditional expression (9), the length of the lens system increases, sothat a compact zoom lens system is not realized.

In the conditional expression (10) regarding the refractive power of thesecond lens unit 2, when the value of fw/|f2| is lower than the lowerlimit of the conditional expression (10), the second lens unit 2 can bemade compact. However, the Petzval sum of the entire system takes alarge negative value, so that curvature of field cannot be correctedonly by selecting a lens material. On the contrary, when the value offw/|f2| exceeds the upper limit of the conditional expression (10),although aberration correction is easy, the length of the zooming systemincreases, so that the compactness the entire system cannot be achieved.

In the conditional expression (11) regarding the refractive power of thethird lens unit 3, when the value of fw/f3 is lower than the lower limitof the conditional expression (11), the refractive power of the thirdlens unit 3 is too strong. For this reason, a back focal length forinserting crystal, etc. cannot be obtained. Further, it is difficult tocorrect spherical aberration. On the contrary, when the value of fw/f3exceeds the upper limit of the conditional expression (11), thecomposite focal length of the first lens unit 1, the second lens unit 2and the third lens unit 3 becomes a diverging system, so that the outerdiameter of the fourth lens unit 4 increases. In addition, the Petzvalsum of the entire system cannot be decreased.

In the conditional expression (12) regarding the refractive power of thefourth lens unit 4, when the value of fw/f4 is lower than the lowerlimit of the conditional expression (12), the coverage is decreased. Insuch a case, in order to obtain a desired coverage, it is necessary thatthe diameter of the first lens unit 1 be sufficiently great, so that thesize and weight reduction cannot be realized. On the contrary, when thevalue of fw/f4 exceeds the upper limit of the condition (12), althoughaberration correction is easy, it is difficult to correct the imbalancein off-axial aberration between during photographing of a near objectand during photographing of a far object.

In, from the object side, the lens element 3a having positive refractivepower, the lens element 3b having positive refractive power and the lenselement 3c having negative refractive power which constitute the thirdlens unit 3, the focal length f31 of the lens element 3a and thecomposite focal length f323 of the lens element 3b and the lens element3c are set by the following conditional expression:

    0.34<f31/|f323|<1.05                     (13)

In the conditional expression (13), when the value of f31/|f323| islower than the lower limit of the condition (13), the diameter of thethird lens unit 3 increases to secure a sufficient f-number. Inaddition, since the back focal length increases, a compact zoom lenssystem cannot be realized. On the contrary, when the value of f31/|f323|exceeds the upper limit of the conditional expression (13), a sufficientback focal length is not obtained although a sufficient f-number issecured.

When the local radius of curvature at an aperture 10% of the effectiveaperture of the object side aspherical surface of the lens element 3a ofthe third lens unit 3 is r311, the local radius of curvature at anaperture 90% of the effective aperture of the object side asphericalsurface of the lens element 3a of the third lens unit 3 is r319, thelocal radius of curvature at an aperture 10% of the effective apertureof the image side aspherical surface of the lens element 3a of the thirdlens unit 3 is r321, the local radius of curvature at an aperture 90% ofthe effective aperture of the image side aspherical surface of the lenselement 3a of the third lens unit 3 is r329, the radius of curvature atan aperture 10% of the effective aperture of the object side asphericalsurface of the lens element 2b of the second lens unit 2 is r211, thelocal radius of curvature at an aperture 90% of the effective apertureof the object side aspherical surface of the lens element 2b of thesecond lens unit 2 is r219, and the object side surface of the lenselement 4(sic) of the fourth lens unit is an aspherical surface, thelocal radius of curvature at an aperture 10% of the effective apertureof the lens element is r411 and the local radius of curvature at anaperture 90% of the effective aperture of the lens element is r419, orthe image side surface of the lens element 4(sic) of the fourth lensunit is an aspherical surface, the local radius of curvature at anaperture 10% of the effective aperture of the lens element is r421 andthe local radius of curvature at an aperture 90% of the effectiveaperture of the lens element is r429, conditional expressions whichdefine the aspherical amount are the following conditional expressions:

    0.412<r311/r319<0.767                                      (21)

    0.193<r321/r329<0.551                                      (22)

    1.059<r211/r219<1.170                                      (23)

and

    0.490<r411/r419<0.787                                      (24)

or

    0.915<r421/r429<1.470                                      (25)

By designing the lens elements so as to satisfy the above-mentionedconditional expressions, a sufficient aberration correcting capabilityis obtained which realizes a high resolution of the zoom lens system.

In the conditional expressions (21) and (22) regarding the asphericalsurfaces of the lens element 3a of the third lens unit 3, when thevalues of r311/r319 and r321/r329 are lower than the lower limits of theconditional expressions (21) and (22), respectively, the correctionamount of spherical aberration is too small. On the contrary, when thevalues of r311/r319 and r321/r329 exceed the upper limits of theconditional expressions (21) and (22), respectively, the correctionamount of spherical aberration is too great, so that sufficientaberration performance is not obtained.

In the conditional expression (23) regarding the object side asphericalsurface of the biconcave lens element 2b of the second lens unit 2, whenthe value of r211/r219 is outside the range between the lower and upperlimits of the conditional expression (23), coma is greatly generated atthe middle position between the wide-angle limit and the telephotolimit, and this causes flare.

In the conditional expression (24) regarding the object side asphericalsurface of the lens element 4a of the fourth lens unit 4, when the valueof r411/r419 is outside the range between the lower and upper limits ofthe condition (24), curvature of field and spherical aberration aregreatly generated, so that sufficient capability is not obtained.

In the conditional expression (25) regarding the image plane 6 sideaspherical surface of the lens element 4a of the fourth lens unit 4,when the value of r421/r429 is outside the range between the lower andupper limits of the conditional expression (25), curvature of field andspherical aberration are greatly generated, so that sufficientcapability is not obtained.

<<First Numerical Example of the First Embodiment>>

A concrete numerical example of the above-mentioned first embodimentshown in FIG. 1 is shown in Table 1 below. In the first numericalexample, the value of (fw×tanω)/(f1×|f2|)^(1/2) is set at 0.2896. Thevalue of fw×|p3c| is set at 0.708.

In Table 1, r represents the radius of curvature of the respective lenselements, d represents the thickness of the lens elements or the airspaces between the lens elements, n represents the refractive index ofthe respective lens elements to the d-line, and υ represents Abbe numberof the respective lens elements to the d-line.

These definitions apply to Table 4, Table 7, Table 10, Table 13, Table16, Table 19 and Table 22 similarly.

                  TABLE 1                                                         ______________________________________                                        Lens   Surface   r        d        n     ν                                 ______________________________________                                               S1        48.280                                                       1a                        0.90     1.50518                                                                             25.4                                        S2        17.748                                                       1b                        4.53     1.60311                                                                             60.7                                        S3        -67.680                                                                                0.20                                                       S4        14.615                                                       1c                        2.67     1.69680                                                                             55.5                                        S5        42.483                                                                       Variable                                                             S6        42.483                                                       2a                        0.60     1.77250                                                                             49.6                                        S7        4.482                                                                                  2.15                                                       S8        -6.474                                                        2b                       0.80     1.66547                                                                             55.2                                        S9        5.874                                                        2c                        1.80     1.80518                                                                             25.4                                        S10       -323.142                                                                     Variable                                                             S11       7.889                                                                                  4.55     1.66547                                                                             55.2                                 3a     S12       -14.939                                                                                0.10                                                       S13       9.748                                                         3b                       2.40     1.51633                                                                             64.1                                        S14       -104.180                                                     3c                        0.60     1.84666                                                                             23.9                                        S15       5.767                                                                        Variable                                                             S16       7.481                                                        4a                        2.87     1.51450                                                                             63.1                                        S17       -31.976                                                                                Variable                                                   S18       ∞                                                      5                         4.30     1.51633                                                                             64.1                                        S19       ∞                                                      ______________________________________                                    

The aspherical configuration is defined by the following expression(26): ##EQU1##

Here, Z is the distance from the vertex of the aspherical surface to apoint on the aspherical surface at a height Y from the optical axis, Yis the height from the optical axis, C is the curvature (=1/r) of thevertex of the aspherical surface, K is a conic constant, and D, E and Fare aspherical coefficients.

The lens surfaces with the surface numbers S8, S11, S12 and S16 areaspherical and their aspherical coefficients are shown in Table 2 below.

                  TABLE 2                                                         ______________________________________                                        Surface                                                                       S8          S11        S12        S16                                         ______________________________________                                        K    -1.30349   -7.99910 ×                                                                         -6.26902 -1.99544 ×                                          10.sup.-1           10.sup.-2                                 D    -6.01825 ×                                                                         -1.39502 ×                                                                         -4.75872 ×                                                                       -2.07422 ×                               10.sup.-4  10.sup.-4  10.sup.-6                                                                              10.sup.-4                                 E    -2.10812 ×                                                                          2.02487 ×                                                                          1.65237 ×                                                                       -6.99987 ×                               10.sup.-5  10.sup.-7  10.sup.-7                                                                              10.sup.-6                                 F    0.0        0.0        0.0      0.0                                       ______________________________________                                    

As an example of the air space which is variable during zooming, valuesat an object point of 2 m are shown in Table 3 below. In this table, thestandard position is a zoom position whereat the magnification borne bythe second lens unit 2 is 1. In the table, f, F/NO and ω represent thefocal lengths, f-numbers and incident half view angles at the wide-anglelimit, the standard position and the telephoto limit, respectively.Moreover, di (i=5, 10, 15, 17) represents the air spaces between thelens elements at the wide-angle limit, the standard position and thetelephoto limit.

These definitions apply to Table 6, Table 9, Table 12, Table 15, Table18, Table 21 and Table 24 similarly.

                  TABLE 3                                                         ______________________________________                                               Wide-angle  Standard Telephoto                                                limit       position limit                                             ______________________________________                                        f        4.825         22.851   44.488                                        F/NO     1.46          2.25     2.67                                          2ω (°)                                                                    59.90         12.73    6.61                                          d5       0.700         9.806    12.450                                        d10      13.383        4.277    1.633                                         d15      6.099         1.666    5.050                                         d17      1.014         5.497    2.063                                         ______________________________________                                    

Concrete values for the conditional expressions (3) to (6) and (13) to(17) in the first numerical example of the embodiment of the inventionare shown below.

    fw/f1=0.222                                                Conditional expression (3)

    fw/|f2|=1.136                            Conditional expression (4)

    fw/f3=0.436                                                Conditional expression (5)

    fw/f4=0.399                                                Conditional expression (6)

    f31/|f323|=0.692                         Conditional expression (13)

    r311/r319=0.518                                            Conditional expression (14)

    r321/r329=0.437                                            Conditional expression (15)

    r211/r219=1.077                                            Conditional expression (16)

    r411/r419=0.690                                            Conditional expression (17)

<<Second Numerical Example of the First Embodiment>>

A second concrete numerical example of the first embodiment is shown inTable 4 below. In the second numerical example, the value of(fw×tanω)/(f1×|f2|)/^(1/2) is set at 0.290. The value of fw×|p3c| is setat 0.643.

                  TABLE 4                                                         ______________________________________                                        Lens   Surface   r        d        n     ν                                 ______________________________________                                               S1        48.297                                                              S1        48.297                                                       1a                        0.90     1.50518                                                                             25.4                                        S2        17.773                                                       1b                        4.53     1.60311                                                                             60.7                                        S3        -67.810                                                                                0.20                                                       S4        14.614                                                       1c                        2.67     1.69680                                                                             55.5                                        S5        42.510                                                                       Variable                                                             S6        42.510                                                       2a                        0.60     1.77250                                                                             49.6                                        S7        4.872                                                                                  2.15                                                       S8        -6.344                                                        2b                       0.80     1.66547                                                                             55.2                                        S9        6.163                                                        2c                        1.80     1.80518                                                                             25.4                                        S10       -187.168                                                                     Variable                                                             S11       7.284                                                                                  4.60     1.66547                                                                             55.2                                 3a     S12       -10.816                                                                                0.10                                                       S13       26.909                                                        3b                       2.40     1.51633                                                                             64.1                                        S14       -60.749                                                      3c                        0.60     1.84666                                                                             23.9                                        S15       6.450                                                                        Variable                                                      4a     S16       7.829                                                                                  2.85     1.51450                                                                             63.1                                        S17       -28.035                                                                      Variable                                                             S18       ∞                                                      5                         4.30     1.51633                                                                             64.1                                        S19       ∞                                                      ______________________________________                                    

The aspherical configuration is defined by the above-describedexpression (26).

The lens surfaces with the surface numbers S8, S11, S12, and S16 areaspherical and their aspherical coefficients are shown in Table 5 below.

                  TABLE 5                                                         ______________________________________                                        Surface                                                                       S8          S11        S12        S16                                         ______________________________________                                        K    -1.59927   -6.64273 ×                                                                         -5.49224 2.83550 ×                                           10.sup.-1           10.sup.-1                                 D    -7.38884 ×                                                                         -2.13723 ×                                                                         2.18903 ×                                                                        -1.89844 ×                               10.sup.-4  10.sup.-4  10.sup.-5                                                                              10.sup.-4                                 E    -2.01243 ×                                                                         -1.52307 ×                                                                         -1.59533 ×                                                                       -1.24516 ×                               10.sup.-5  10.sup.-7  10.sup.-8                                                                              10.sup.-5                                 F    0.0        0.0        0.0      0.0                                       ______________________________________                                    

As an example of the air space which is variable during zooming, valuesat an object point of 2 m are shown in Table 6 below. In this table, thestandard position is a zoom position whereat the magnification borne bythe second lens unit 2 is 1.

                  TABLE 6                                                         ______________________________________                                               Wide-angle  Standard Telephoto                                                limit       position limit                                             ______________________________________                                        f        4.900         23.287   45.100                                        F/NO     1.48          2.30     2.71                                          2ω (°)                                                                    59.13         12.49    6.52                                          d5       0.700         9.807    12.450                                        d10      13.383        4.276    1.633                                         d15      6.099         1.468    4.958                                         d17      1.000         5.631    2.141                                         ______________________________________                                    

Concrete values for the conditional expressions (3) to (6) and (13) to(17) in the second numerical example are shown below.

    fw/f1=0.226                                                Conditional expression (3)

    fw/|f2|=1.155                            Conditional expression (4)

    fw/f3=0.442                                                Conditional expression (5)

    fw/f4=0.401                                                Conditional expression (6)

    f31/|f323|=0.821                         Conditional expression (13)

    r311/r319=0.412                                            Conditional expression (14)

    r321/r329=0.193                                            Conditional expression (15)

    r211/r219=1.059                                            Conditional expression (16)

    r411/r419=0.490                                            Conditional expression (17)

<<Third Numerical Example of the First Embodiment>>

A third concrete numerical example of the first embodiment is shown inTable 7 below. In the third numerical example, the value of(fw×tanω)/(f1×|f2|)^(1/2) is set at 0.289. The value of fw×|p3c| is setat 0.799.

                  TABLE 7                                                         ______________________________________                                        Lens   Surface   r        d        n     ν                                 ______________________________________                                               S1        48.011                                                       1a                        0.90     1.50518                                                                             25.4                                        S2        17.638                                                       1b                        4.53     1.60311                                                                             60.7                                        S3        -68.747                                                                                0.20                                                       S4        14.582                                                       1c                        2.67     1.69680                                                                             55.5                                        S5        42.499                                                                       Variable                                                             S6        42.499                                                       2a                        0.60     1.77250                                                                             49.6                                        S7        4.807                                                                                  2.15                                                       S8        -6.623                                                        2b                       0.80     1.66547                                                                             55.2                                        S9        5.464                                                        2c                        1.80     1.80518                                                                             25.4                                        S10       ∞                                                                                Variable                                                   S11       10.798                                                                                 3.70     1.66547                                                                             55.2                                 3a     S12       -17.447                                                                                0.11                                                       S13       6.048                                                         3b                       3.00     1.51633                                                                             64.1                                        S14       246.866                                                      3c                        0.60     1.84666                                                                             23.9                                        S15       5.113                                                                        Variable                                                             S16       7.340                                                        4a                        2.87     1.51450                                                                             63.1                                        S17       -35.699                                                                                Variable                                                   S18       ∞                                                      5                         4.30     1.51633                                                                             64.1                                        S19       ∞                                                      ______________________________________                                    

The aspherical configuration is defined by the above-describedexpression (26).

The lens surfaces with the surface numbers S8, S11, S12 and S16 areaspherical and their aspherical coefficients are shown in Table 8 below.

                  TABLE 8                                                         ______________________________________                                        Surface                                                                       S8          S11        S12        S16                                         ______________________________________                                        K    -7.86417 ×                                                                         -1.03290   -4.36782 ×                                                                        1.68183 ×                               10.sup.-1             10.sup.-1                                                                              10.sup.-1                                 D    -3.84920 ×                                                                         -3.58814 ×                                                                          9.82512 ×                                                                       -3.87598 ×                               10.sup.-4  10.sup.-5  10.sup.-5                                                                              10.sup.-4                                 E    -2.72545 ×                                                                          7.19110 ×                                                                          1.50306 ×                                                                       -6.13115 ×                               10.sup.-5  10.sup.-7  10.sup.-7                                                                              10.sup.-6                                 F    0.0        0.0        0.0      0.0                                       ______________________________________                                    

As an example of the air space which is variable during zooming, valuesat an object point of 2 m are shown in Table 9 below. In this table, thestandard position is a zoom position whereat the magnification borne bythe second lens unit 2 is 1.

                  TABLE 9                                                         ______________________________________                                               Wide-angle  Standard Telephoto                                                limit       position limit                                             ______________________________________                                        f        4.825         23.088   44.488                                        F/NO     1.46          2.28     2.67                                          2ω (°)                                                                    59.83         12.64    6.58                                          d5       0.700         9.806    12.450                                        d10      13.383        3.677    1.633                                         d15      6.099         1.666    5.050                                         d17      1.014         5.497    2.063                                         ______________________________________                                    

Concrete values for the conditional expressions (3) to (6) and (13) to(17) in the third numerical example are shown below.

    fw/f1=0.222                                                Conditional expression (3)

    fw/|f2|=1.136                            Conditional expression (4)

    fw/f3=0.438                                                Conditional expression (5)

    fw/f4=0.398                                                Conditional expression (6)

    f31/|f323|=0.492                         Conditional expression (13)

    r311/r319=0.767                                            Conditional expression (14)

    r321/r329=0.206                                            Conditional expression (15)

    r211/r219=1.130                                            Conditional expression (16)

    r411/r419=0.687                                            Conditional expression (17)

<<Fourth Numerical Example of the First Embodiment>>

A fourth concrete numerical example of the first embodiment is shown inTable 10 below. In the fourth numerical example, the value of(fw×tanω)/(f1×|f2|)^(1/2) is set at 0.289. The value of fw×|p3c| is setat 0.754.

                  TABLE 10                                                        ______________________________________                                        Lens   Surface   r        d        n     ν                                 ______________________________________                                               S1        48.011                                                       1a                        0.90     1.50518                                                                             25.4                                        S2        17.638                                                       1b                        4.53     1.60311                                                                             60.7                                        S3        -68.747                                                                                0.20                                                       S4        14.582                                                       1c                        2.67     1.69680                                                                             55.5                                        S5        42.499                                                                       Variable                                                             S6        42.499                                                       2a                        0.60     1.77250                                                                             49.6                                        S7        4.807                                                                                  2.15                                                       S8        -6.623                                                        2b                       0.80     1.66547                                                                             55.2                                        S9        5.464                                                        2c                        1.80     1.80518                                                                             25.4                                        S10       ∞                                                                                Variable                                                   S11       9.901                                                                                  3.80     1.66547                                                                             55.2                                 3a     S12       -17.801                                                                                0.10                                                       S13       6.827                                                         3b                       3.00     1.51633                                                                             64.1                                        S14       235.691                                                      3c                        0.60     1.84666                                                                             23.9                                        S15       5.416                                                                        Variable                                                             S16       7.340                                                        4a                        0.60     1.51450                                                                             63.1                                        S17       -35.699                                                                                Variable                                                   S18       ∞                                                      5                         4.30     1.51633                                                                             64.1                                        S19       ∞                                                      ______________________________________                                    

The aspherical configuration is defined by the above-describedexpression (26).

The lens surfaces with the surface numbers S8, S11, S12 and S16 areaspherical and their aspherical coefficients are shown in Table 11below.

                  TABLE 11                                                        ______________________________________                                        Surface                                                                       S8          S11        S12        S16                                         ______________________________________                                        K    -7.86417 ×                                                                         -9.88732 ×                                                                         -4.36782 ×                                                                        1.68183 ×                               10.sup.-1  10.sup.-1  10.sup.-1                                                                              10.sup.-1                                 D    -3.84920 ×                                                                         -3.17578 ×                                                                          1.18295 ×                                                                       -3.87598 ×                               10.sup.-4  10.sup.-5  10.sup.-4                                                                              10.sup.-4                                 E    -2.72545 ×                                                                          5.20658 ×                                                                          3.10261 ×                                                                       -6.13115 ×                               10.sup.-5  10.sup.-7  10.sup.-8                                                                              10.sup.-6                                 F    0.0        0.0        0.0      0.0                                       ______________________________________                                    

As an example of the air space which is variable during zooming, valuesat an object point of 2 m are shown in Table 12 below. In this table,the standard position is a zoom position whereat the magnification borneby the second lens unit 2 is 1.

                  TABLE 12                                                        ______________________________________                                               Wide-angle  Standard Telephoto                                                limit       position limit                                             ______________________________________                                        f        4.825         23.013   44.486                                        F/NO     1.46          2.27     2.67                                          2ω (°)                                                                    59.73         12.67    6.58                                          d5       0.700         9.806    12.450                                        d10      13.383        4.277    1.633                                         d15      6.099         1.666    5.050                                         d17      1.014         5.497    2.063                                         ______________________________________                                    

Concrete values for the conditional expressions (3) to (6) and (13) to(17) in the fourth numerical example are shown below.

    fw/f1=0.222                                                Conditional expression (3)

    fw/|f2|=1.136                            Conditional expression (4)

    fw/f3=0.438                                                Conditional expression (5)

    fw/f4=0.398                                                Conditional expression (6)

    f31/|f323|=0.528                         Conditional expression (13)

    r311/r319=0.718                                            Conditional expression (14)

    r321/r329=0.277                                            Conditional expression (15)

    r211/r219=1.170                                            Conditional expression (16)

    r411/r419=0.687                                            Conditional expression (17)

<<Fifth Numerical Example of the First Embodiment>>

A fifth concrete numerical example of the first embodiment is shown inTable 13 below. In the fifth numerical example, the value of(fw×tanω)/(f1×|f2|)^(1/2) is set at 0.255. The value of fw×|p3c| is setat 0.729.

                  TABLE 13                                                        ______________________________________                                        Lens   Surface   r        d        n     ν                                 ______________________________________                                               S1        50.914                                                       1a                        0.90     1.50518                                                                             25.4                                        S2        18.815                                                       1b                        4.38     1.60311                                                                             60.7                                        S3        -62.375                                                                                0.20                                                       S4        14.300                                                       1c                        2.50     1.69680                                                                             55.5                                        S5        33.778                                                                       Variable                                                             S6        33.778                                                       2a                        0.60     1.77250                                                                             49.6                                        S7        4.871                                                                                  2.38                                                       S8        -6.100                                                        2b                       0.80     1.66547                                                                             55.2                                        S9        7.007                                                        2c                        1.68     1.80518                                                                             25.4                                        S10       -53.117                                                                      Variable                                                             S11       9.271                                                                                  4.26     1.66547                                                                             55.2                                 3a     S12       -17.003                                                                                0.10                                                       S13       7.638                                                         3b                       2.81     1.51633                                                                             64.1                                        S14       -171.455                                                     3c                        0.60     1.84666                                                                             23.9                                        S15       5.623                                                                        Variable                                                             S16       7.940                                                        4a                        2.65     1.51450                                                                             63.1                                        S17       -35.233                                                                                Variable                                                   S18       ∞                                                      5                         4.30     1.51633                                                                             64.1                                        S19       ∞                                                      ______________________________________                                    

The aspherical configuration is defined by the above-describedexpression (26).

The lens surfaces with the surface numbers S8, S11, S12 and S16 areaspherical and their aspherical coefficients are shown in Table 14below.

                  TABLE 14                                                        ______________________________________                                        Surface                                                                       S8          S11        S12        S16                                         ______________________________________                                        K     1.19086   -6.52397 ×                                                                         -7.30379  3.06179 ×                                          10.sup.-1           10.sup.-1                                 D     6.76360 ×                                                                         -9.97655 ×                                                                         -2.08333 ×                                                                       -2.43589 ×                               10.sup.-4  10.sup.-5  10.sup.-5                                                                              10.sup.-4                                 E     3.84156 ×                                                                         -3.13284 ×                                                                         -3.28248 ×                                                                       -9.73397 ×                               10.sup.-5  10.sup.-7  10.sup.-8                                                                              10.sup.-6                                 F    -3.58630 ×                                                                         0.0        0.0       1.33719 ×                               10.sup.-7                      10.sup.-7                                 ______________________________________                                    

As an example of the air space which is variable during zooming, valuesat an object point of 2 m are shown in Table 15 below. In this table,the standard position is a zoom position whereat the magnification borneby the second lens unit 2 is 1.

                  TABLE 15                                                        ______________________________________                                               Wide-angle  Standard Telephoto                                                limit       position limit                                             ______________________________________                                        f        4.841         23.311   45.005                                        F/NO     1.46          2.27     2.72                                          2ω (°)                                                                    59.82         12.52    6.52                                          d5       0.700         10.440   13.218                                        d10      14.010        4.270    1.492                                         d15      6.063         1.423    4.824                                         d17      1.015         5.655    2.254                                         ______________________________________                                    

Concrete values for the conditional expressions (3) to (6) and (13) to(17) in the fifth numerical example are shown below.

    fw/f1=0.213                                                Conditional expression (3)

    fw/|f2|=1.082                            Conditional expression (4)

    fw/f3=0.434                                                Conditional expression (5)

    fw/f4=0.376                                                Conditional expression (6)

    f31/|f323|=0.764                         Conditional expression (13)

    r311/r319=0.491                                            Conditional expression (14)

    r321/r329=0.551                                            Conditional expression (15)

    r211/r219=1.080                                            Conditional expression (16)

    r411/r419=0.787                                            Conditional expression (17)

<<Sixth Numerical Example of the First Embodiment>>

A sixth concrete numerical example of the first embodiment is shown inTable 16 below. In the sixth numerical example, the value of(fw×tanω)/(f1×|f2|)^(1/2) is set at 0.301. The value of fw×|p3c| is setat 0.671.

                  TABLE 16                                                        ______________________________________                                        Lens   Surface   r        d        n     ν                                 ______________________________________                                               S1        40.774                                                       1a                        0.90     1.50518                                                                             25.4                                        S2        16.433                                                       1b                        4.51     1.60311                                                                             60.7                                        S3        -87.094                                                                                0.20                                                       S4        14.613                                                       1c                        2.72     1.69680                                                                             55.5                                        S5        51.625                                                                       Variable                                                             S6        32.716                                                       2a                        0.65     1.77250                                                                             49.6                                        S7        4.548                                                                                  2.13                                                       S8        -5.797                                                        2b                       0.80     1.66547                                                                             55.2                                        S9        5.960                                                        2c                        1.74     1.80518                                                                             25.4                                        S10       -111.219                                                                     Variable                                                             S11       7.650                                                                                  4.75     1.66547                                                                             55.2                                 3a     S12       -12.559                                                                                0.10                                                       S13       13.505                                                        3b                       2.63     1.51633                                                                             64.1                                        S14       -42.751                                                      3c                        0.60     1.84666                                                                             23.9                                        S15       6.616                                                                        Variable                                                             S16       7.791                                                        4a                        0.60     1.51450                                                                             63.1                                        S17       -27.282                                                                                Variable                                                   S18       ∞                                                      5                         4.30     1.51633                                                                             64.1                                        S19       ∞                                                      ______________________________________                                    

The aspherical configuration is defined by the above-describedexpression (26).

The lens surfaces with the surface numbers S8, S11, S12 and S16 areaspherical and their aspherical coefficients are shown in Table 17below.

                  TABLE 17                                                        ______________________________________                                        Surface                                                                       S8          S11        S12        S16                                         ______________________________________                                        K    -1.08836   -7.19076 ×                                                                         -6.66558  2.88131 ×                                          10.sup.-1  10.sup.-5                                                                              10.sup.-1                                 D    -6.47949 ×                                                                         -1.76611 ×                                                                         -3.12888 ×                                                                       -1.97219 ×                               10.sup.-4  10.sup.-4  10.sup.-5                                                                              10.sup.-4                                 E    -1.42550 ×                                                                         -2.86321 ×                                                                          4.91724 ×                                                                       -1.38847 ×                               10.sup.-5  10.sup.-7  10.sup.-7                                                                              10.sup.-5                                 F    -2.07217 ×                                                                          4.77300 ×                                                                         -1.97368 ×                                                                        1.03917 ×                               10.sup.-6  10.sup.-9  10.sup.-9                                                                              10.sup.-7                                 ______________________________________                                    

As an example of the air space which is variable during zooming, valuesat an object point of 2 m are shown in Table 18 below. In this table,the standard position is a zoom position whereat the magnification borneby the second lens unit 2 is 1.

                  TABLE 18                                                        ______________________________________                                               Wide-angle  Standard Telephoto                                                limit       position limit                                             ______________________________________                                        f        4.859         22.903   45.123                                        F/NO     1.47          2.28     2.70                                          2ω (°)                                                                    59.31         12.64    6.52                                          d5       0.700         9.436    11.953                                        d10      13.260        4.524    2.007                                         d15      6.179         1.501    4.998                                         d17      1.014         5.691    2.194                                         ______________________________________                                    

Concrete values for the conditional expressions (3) to (6) and (13) to(17) in the sixth numerical example are shown below.

    fw/f1=0.232                                                Conditional expression (3)

    fw/|f2|=1.205                            Conditional expression (4)

    fw/f3=0.453                                                Conditional expression (5)

    fw/f4=0.401                                                Conditional expression (6)

    f31/|f323|=0.764                         Conditional expression (13)

    r311/r319=0.470                                            Conditional expression (14)

    r321/r329=0.278                                            Conditional expression (15)

    r211/r219=1.084                                            Conditional expression (16)

    r411/r419=0.688                                            Conditional expression (17)

<<Seventh Numerical Example of the First Embodiment>>

A seventh concrete numerical example of the first embodiment is shown inTable 19 below. In the seventh numerical example, the value of(fw×tanω)/(f1×|f2|)^(1/2) is set at 0.302. The value of fw×|p3c| is setat 0.688.

                  TABLE 19                                                        ______________________________________                                        Lens   Surface   r        d        n     ν                                 ______________________________________                                               S1        42.522                                                       1a                        0.90     1.50518                                                                             25.4                                        S2        16.588                                                       1b                        4.60     1.60311                                                                             60.7                                        S3        -78.767                                                                                0.20                                                       S4        14.517                                                       1c                        2.75     1.69680                                                                             55.5                                        S5        49.892                                                                       Variable                                                             S6        49.892                                                       2a                        0.65     1.77250                                                                             49.6                                        S7        4.737                                                                                  2.11                                                       S8        -96.414                                                       2b                       0.80     1.66547                                                                             55.2                                        S9        5.559                                                        2c                        2.00     1.80518                                                                             25.4                                        S10       -684.342                                                                     Variable                                                             S11       8.051                                                                                  4.75     1.66547                                                                             55.2                                 3a     S12       -14.512                                                                                0.10                                                       S13       10.321                                                        3b                       2.65     1.51633                                                                             64.1                                        S14       -59.609                                                      3c                        0.65     1.84666                                                                             23.9                                        S15       5.982                                                                        Variable                                                             S16       7.542                                                        4a                        2.75     1.51450                                                                             63.1                                        S17       -33.034                                                                                Variable                                                   S18       ∞                                                      5                         4.0      1.51633                                                                             64.1                                        S19       ∞                                                      ______________________________________                                    

The aspherical configuration is defined by the above-describedexpression (26).

The lens surfaces with the surface numbers S8, S11, S12 and S16 areaspherical and their aspherical coefficients are shown in Table 20below.

                  TABLE 20                                                        ______________________________________                                        Surface                                                                       S8         S11         S12       S16                                          ______________________________________                                        K    -2.32385 ×                                                                        -8.67603 × 10.sup.-1                                                                -6.96549                                                                                2.51517 × 10.sup.-1                     10.sup.-1                                                                D    -9.56378 ×                                                                        -1.37144 × 10.sup.-4                                                                -5.22471 ×                                                                      -2.57487 × 10.sup.-4                      10.sup.-5             10.sup.-5                                          E    -2.33087 ×                                                                          2.13051 × 10.sup.-7                                                               4.87115 ×                                                                       -1.08193 × 10.sup.-5                      10.sup.-5             10.sup.-7                                          F    0.0       0.0         0.0     0.0                                        ______________________________________                                    

As an example of the air space which is variable during zooming, valuesat an object point of 2 m are shown in Table 21 below. In this table,the standard position is a zoom position whereat the magnification borneby the second lens unit 2 is 1.

                  TABLE 21                                                        ______________________________________                                        Wide-angle limit                                                                              Standard position                                                                         Telephoto limit                                   ______________________________________                                        f     4.862         22.814      45.113                                        F/NO  1.52          2.30        2.80                                          2ω (°)                                                                 59.53         12.80       6.54                                          d5    0.700         9.440       11.954                                        d10   13.260        4.520       1.006                                         d15   6.380         1.719       5.192                                         d17   1.015         5.976       2.202                                         ______________________________________                                    

Concrete values for the conditional expressions (3) to (6) and (13) to(17) in the seventh numerical example are shown below.

    fw/f1=0.232                                                Conditional expression (3)

    fw/|f2|=1.205                            Conditional expression (4)

    fw/f3=0.448                                                Conditional expression (5)

    fw/f4=0.398                                                Conditional expression (6)

    f31/|f323|=0.696                         Conditional expression (13)

    r311/r319=0.504                                            Conditional expression (14)

    r321/r329=0.434                                            Conditional expression (15)

    r211/r219=1.128                                            Conditional expression (16)

    r411/r419=0.676                                            Conditional expression (17)

<<Eighth Numerical Example of the First Embodiment>>

An eighth concrete numerical example of the first embodiment is shown inTable 22 below. In the eighth numerical example, the value of(fw×tanω)/(f1×|f2|)^(1/2) is set at 0.290. The value of fw×|p3c is setat 0.708.

                  TABLE 22                                                        ______________________________________                                        Lens   Surface   r        d        n     υ                            ______________________________________                                               S1        48.280                                                       1a                        0.90     1.50518                                                                             25.4                                        S2        17.748                                                       1b                        4.53     1.60311                                                                             60.7                                        S3        -67.680                                                                                0.20                                                       S4        14.615                                                       1c                        2.67     1.69680                                                                             55.5                                        S5        42.483                                                                                 Variable                                                   S6        42.483                                                       2a                        0.60     1.77250                                                                             49.6                                        S7        4.842                                                                                  2.15                                                       S8        -6.474                                                       2b                        0.80     1.66547                                                                             55.2                                        S9        5.874                                                        2c                        1.80     1.80518                                                                             25.4                                        S10       -14.880                                                                                Variable                                                   S11       7.906                                                        3a                        4.55     1.66547                                                                             55.2                                        S12       -14.880                                                                                0.10                                                       S13       9.753                                                        3b                        2.40     1.51633                                                                             64.1                                        S14       -104.180                                                     3c                        0.60     1.84666                                                                             23.9                                        S15       7.767                                                                                  Variable                                                   S16       7.487                                                        4a                        2.87     1.51450                                                                             63.1                                        S17       -32.099                                                                                Variable                                                   S18       ∞                                                      5                         4.30     1.51633                                                                             64.1                                        S19       ∞                                                      ______________________________________                                    

The aspherical configuration is defined by the above-describedexpression (26).

The lens surfaces with the surface numbers S8, S11, S12 and S17 areaspherical and their aspherical coefficients are shown in Table 23below.

                  TABLE 23                                                        ______________________________________                                        Surface                                                                       S8         S11         S12       S17                                          ______________________________________                                        K    -1.30349  -7.88646 × 10.sup.-1                                                                -6.28638                                                                              -3.39558 × 10.sup.-2                 D    -6.01825 ×                                                                        -1.39605 × 10.sup.-4                                                                3.77147 ×                                                                        `3.36145 × 10.sup.-4                     10.sup.-4             10.sup.-6                                          E    -2.10812 ×                                                                          2.67960 × 10.sup.-7                                                               1.19995 ×                                                                         3.53837 × 10.sup.-6                     10.sup.-5             10.sup.-7                                          F    0.0       0.0         0.0     0.0                                        ______________________________________                                    

As an example of the air space which is variable during zooming, valuesat an object point of 2 m are shown in Table 24 below. In this table,the standard position is a zoom position whereat the magnification borneby the second lens unit 2 is 1.

                  TABLE 24                                                        ______________________________________                                        Wide-angle limit                                                                              Standard position                                                                         Telephoto limit                                   ______________________________________                                        f     4.825         22.851      44.488                                        F/NO  1.46          2.25        2.67                                          2ω (°)                                                                 59.96         12.62       6.59                                          d5    0.700         9.806       12.450                                        d10   12.783        3.677       1.033                                         d15   6.099         1.666       5.050                                         d17   1.014         5.497       2.063                                         ______________________________________                                    

Concrete values for the conditional expressions (3) to (6), (13) to (16)and (18) in the eighth numerical example are shown below.

    fw/f1=0.222                                                Conditional expression (3)

    fw/|f2|=1.136                            Conditional expression (4)

    fw/f3=0.436                                                Conditional expression (5)

    fw/f4=0.399                                                Conditional expression (6)

    f31/|f323|=0.691                         Conditional expression (13)

    r311/r319=0.529                                            Conditional expression (14)

    r321/r329=0.413                                            Conditional expression (15)

    r211/r219=1.078                                            Conditional expression (16)

    r421/r429=1.078                                            Conditional expression (18)

<<Aberration Performance of the Numerical Examples of the FirstEmbodiment>>

FIG. 3, FIG. 4 and FIG. 5 are representations of aberration curvesshowing aberration capability of the aspherical zoom lens system in theabove-mentioned first numerical example of the first embodiment.

FIG. 6, FIG. 7 and FIG. 8 show aberration capability of the asphericalzoom lens system in the above-mentioned second numerical example of thefirst embodiment.

FIG. 9, FIG. 10 and FIG. 11 show aberration capability of the asphericalzoom lens system in the above-mentioned third numerical example of thefirst embodiment.

FIG. 12, FIG. 13 and FIG. 14 show aberration capability of theaspherical zoom lens system in the above-mentioned fourth numericalexample of the first embodiment.

FIG. 15, FIG. 16 and FIG. 17 show aberration capability of theaspherical zoom lens system in the above-mentioned fifth numericalexample of the first embodiment.

FIG. 18, FIG. 19 and FIG. 20 show aberration capability of theaspherical zoom lens system in the above-mentioned sixth numericalexample of the first embodiment.

FIG. 21, FIG. 22 and FIG. 23 show aberration capability of theaspherical zoom lens system in the above-mentioned seventh numericalexample of the first embodiment.

FIG. 24, FIG. 25 and FIG. 26 show aberration capability of theaspherical zoom lens system in the above-mentioned eighth numericalexample of the first embodiment.

In these figures, (a) is a drawing of spherical aberration, wherein thesolid line represents the value to the d-line and the dotted linerepresents the sine condition; (b) is a drawing of astigmatism, whereinthe solid line represents the sagittal curvature of field and the dottedline represents the meridional curvature of field; (c) is a drawing ofdistortion aberration and (d) is a drawing of axial aberration, whereinthe solid line, the dotted line and the broken line represent the valuesto the d-line, the F-line and the C-line, respectively; (e) is a drawingof chromatic aberration of magnification, wherein the dotted line andthe broken line represent the values to the F-line and the C-line,respectively. From these figures, it is apparent that the zoom lenssystems according to the above-mentioned eight concrete numericalexamples of the embodiment have excellent optical capability.

<<Numerical Example of the Second Embodiment>>

A concrete numerical example of the second embodiment is shown in Table25 below. In this numerical example, the value of(fw×tanω)/(f1×|f2|)^(1/2) is set at 0.289. The value of fw×|p3c| is setat 0.652.

In Table 25, r represents the radius of curvature of the respective lenselements, d represents the thickness of the lens elements or the airspaces between the lens elements, n represents the refractive index ofthe respective lens elements to the d-line, and υ represents Abbe numberof the respective lens elements to the d-line.

                  TABLE 25                                                        ______________________________________                                        Lens   Surface   r        d        n     υ                            ______________________________________                                               S1        48.298                                                       1a                        0.90     1.50518                                                                             25.4                                        S2        17.769                                                       1b                        4.53     1.60311                                                                             60.7                                        S3        -67.792                                                                                0.20                                                       S4        14.615                                                       1c                        2.67     1.69680                                                                             55.5                                        S5        42.519                                                                                 Variable                                                   S6        42.519                                                       2a                        0.60     1.77250                                                                             49.6                                        S7        4.840                                                                                  2.15                                                       S8        -6.475                                                       2b                        0.80     1.66547                                                                             55.2                                        S9        5.884                                                        2c                        1.80     1.80518                                                                             25.4                                        S10       -317.238                                                                               Variable                                                   S11       7.718                                                        3a                        4.60     1.66547                                                                             55.2                                        S12       -12.767                                                                                0.10                                                       S13       15.123                                                       3b                        2.40     1.51633                                                                             64.1                                        S14       -37.470                                                                                0.10                                                       S15       -47.282                                                      3c                        0.60     1.84666                                                                             23.9                                        S16       6.340                                                                                  Variable                                                   S17       8.043                                                        4a                        2.50     1.51450                                                                             63.1                                        S18       -25.947                                                                                Variable                                                   S19       ∞                                                      5                         4.0      1.51633                                                                             64.1                                        S20       ∞                                                      ______________________________________                                    

The aspherical configuration is defined by the above-describedexpression (26).

The lens surfaces with the surface numbers S8, S11, S12 and S17 areaspherical and their aspherical coefficients are shown in Table 26below.

                  TABLE 26                                                        ______________________________________                                        Surface                                                                       S8         S11         S12       S17                                          ______________________________________                                        K    -1.46313  -7.54703 × 10.sup.-1                                                                -6.04953                                                                                2.92653 × 10.sup.-1                D    -6.71083 ×                                                                        -1.78353 × 10.sup.-4                                                                2.71911 ×                                                                       -2.24651 × 10.sup.-4                      10.sup.-4             10.sup.-6                                          E    -2.14482 ×                                                                          9.08433 × 10.sup.-8                                                               8.94155 ×                                                                       -9.28589 × 10.sup.-6                      10.sup.-5             10.sup.-8                                          F    0.0       0.0         0.0     0.0                                        ______________________________________                                    

As an example of the air space which is variable during zooming, valuesat an object point of 2 m are shown in Table 27 below. In this table,the standard position is a zoom position whereat the magnification borneby the second lens unit 2 is 1. In the table, f, F/NO and ω representthe focal lengths, f-numbers and incident half view angles at thewide-angle limit, the standard position and the telephoto limit,respectively. Moreover, di (i=5, 10, 16, 18) represents the air spacesbetween the lens elements at the wide-angle limit, the standard positionand the telephoto limit.

                  TABLE 27                                                        ______________________________________                                               Wide-angle  Standard Telephoto                                                limit       position limit                                             ______________________________________                                        f        4.886         23.143   44.946                                        F/NO     1.49          2.28     2.70                                          2ω (°)                                                                    59.23         12.52    6.53                                          d5       0.700         9.807    12.450                                        d10      13.389        4.276    1.633                                         d15      6.099         1.501    4.968                                         d17      1.000         5.598    2.132                                         ______________________________________                                    

Concrete values for the conditional expressions (3) to (6) and (13) to(17) in the numerical example of the second embodiment are shown below.

    fw/f1=0.225                                                Conditional expression (3)

    fw/|f2|=1.151                            Conditional expression (4)

    fw/f3=0.441                                                Conditional expression (5)

    fw/f4=0.399                                                Conditional expression (6)

    f31/|f323|=0.747                         Conditional expression (13)

    r311/r319=0.529                                            Conditional expression (14)

    r321/r329=0.290                                            Conditional expression (15)

    r211/r219=1.108                                            Conditional expression (16)

    r411/r419=0.681                                            Conditional expression (17)

FIG. 27, FIG. 28 and FIG. 29 show aberration capability of theaspherical zoom lens system in the numerical example of the secondembodiment.

In these figures, (a) is a drawing of spherical aberration, wherein thesolid line represents the value to the d-line and the dotted linerepresents the sine condition; (b) is a drawing of astigmatism, whereinthe solid line represents the sagittal curvature of field and the dottedline represents the meridional curvature of field; (c) is a drawing ofdistortion aberration and (d) is a drawing of axial aberration, whereinthe solid line, the dotted line and the broken line represent the valuesto the d-line, the F-line and the C-line, respectively; (e) is a drawingof chromatic aberration of magnification, wherein the dotted line andthe broken line represent the values to the F-line and the C-line,respectively. From these figures, it is apparent that the zoom lenssystem according to the above-mentioned concrete numerical example ofthe embodiment have excellent optical capability.

<<Third Embodiment>>

<Embodiment of a Video Camera, Etc.>

FIG. 30 is a view showing the structure of a video camera using a zoomlens system of the present invention. In the figure, a zoom lens system301 is structured like the above-described embodiments, and in addition,a low-pass filter 302, an image pickup element 303, a microphone 304, asignal processing circuit 305, a viewfinder 306, an audio monitor 307and a recording system 308 are basically included. Further, anadditional function may be provided.

FIG. 31 is a view showing the structure of an electronic still camerausing a zoom lens system of the present invention. In the figure, a zoomlens system 311 is structured like the above-described embodiments, andin addition, a low-pass filter 312, an image pickup element 313, asignal processing circuit 314, a liquid crystal monitor 315 and arecording system 316 are included. The recording system 316 has thefunction of recording photographic conditions as well as subject images.Further, an additional function may be provided.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been changed in the details ofconstruction and the combination and arrangement of parts may beresorted to without departing from the scope and the sprite of theinvention as hereinafter claimed.

INDUSTRIAL APPLICABILITY

In the zoom lens system of the present invention, a compact andhigh-performance aspherical zoom lens system with an f-number ofapproximately 1.4, an angle of view of 59 degree or greater and a zoomratio of approximately 10× is realized with as few as ten lens elements.Therefore, by using such a zoom lens system in a video camera and anelectronic still camera, such a product may be realized that is compactin size, light in weight and has high performance.

We claim:
 1. A zoom lens system comprising from the side of an objectwhich is a subject: a first lens unit having positive refractive powerand fixed in relation to an image plane; a second lens unit havingnegative refractive power and performing zooming by moving along anoptical axis; a third lens unit having positive refractive power whichis fixed in relation to the image plane and performs condensing; and afourth lens unit having positive refractive power which moves along theoptical axis so that the image plane, which varies responding to themovement of said second lens unit and a movement of the object which isthe subject, is maintained in a certain position in relation to areference plane,wherein said first lens unit comprises from said objectside: a first lens element of the first lens unit having negativerefractive power; a second lens element of the first lens unit havingpositive refractive power; and a meniscus lens element having positiverefractive power and being convex to the object side; wherein saidsecond lens unit comprises from said object side: a first lens elementof the second lens unit having negative refractive power; a second,biconcave lens element having negative refractive power; and a thirdlens element of the second lens unit having positive refractive powerand being convex to the object side surface connected to said biconcavelens element, at least one of the surfaces of said lens elements of saidsecond lens unit being aspherical, wherein said third lens unitcomprises from the object side: a first lens element of the third lensunit having positive refractive power; a second lens element of thethird lens unit having positive refractive power; and a third lenselement of the third lens unit having negative refractive power, atleast one of the surfaces of said lens elements of said third lens unitbeing aspherical, wherein said fourth lens unit comprises at least onelens element of the fourth lens unit, at least one of the surfaces ofsaid lens element of said fourth lens unit being aspherical, wherein, fwis the focal length of the zoom lens system at the wide-angle limit, fi(i=1, 2, 3, 4) is the focal length of an ith lens unit, ω is the halfview angle at the wide-angle limit and p3c is the refractive power ofthe image side surface of said third lens element of the third lensunit, the following is satisfied:

    0.255<(fw×tanω)/(f1×|f2|).sup.1/2 <0.301;

    0.643<fw×|p3c|<0.799;

    0.212<fw/f1<0.232;

    1.081<fw/|f2|<1.205;

    0.434<fw/f3<0.453; and

    0.376<fw/f4<0.421.


2. 2. A video camera using a zoom lens system according to claim
 1. 3.An electronic still camera using a zoom lens system according toclaim
 1. 4. A zoom lens system comprising from the side of an objectwhich is a subject: a first lens unit having positive refractive powerand fixed in relation to an image plane; a second lens unit havingnegative refractive power and performing zooming by moving along anoptical axis; a third lens unit having positive refractive power whichis fixed in relation to the image plane and performs condensing; and afourth lens unit having positive refractive power which moves along theoptical axis so that the image plane, which varies responding to themovement of said second lens unit and a movement of the object which isthe subject, is maintained in a certain position in relation to areference plane,wherein said first lens unit comprises from said objectside: a first lens element of the first lens unit having negativerefractive power; a second lens element of the first lens unit havingpositive refractive power; and a meniscus lens element having positiverefractive power and being convex to the object side; wherein saidsecond lens unit comprises from said object side: a first lens elementof the second lens unit having negative refractive power; a second,biconcave lens element having negative refractive power; and a thirdlens element of the second lens unit having positive refractive powerand being convex to the object side surface connected to said biconcavelens element, at least one of the surfaces of said lens elements of saidsecond lens unit being aspherical, wherein said third lens unitcomprises from the object side: a first lens element of the third lensunit having positive refractive power; a second lens element of thethird lens unit having positive refractive power; and a third lenselement of the third lens unit having negative refractive power, atleast one of the surfaces of said lens elements of said third lens unitbeing aspherical, wherein said fourth lens unit comprises at least onelens element of the fourth lens unit, at least one of the surfaces ofsaid lens element of said fourth lens unit being aspherical, wherein, insaid third lens unit, said first lens element of the third lens unit isa biconvex lens and said third lens element of the third lens unit isdisposed so as to be concave to the image side, wherein, when fw is thefocal length of the zoom lens system at the wide-angle limit, fi (i=1,2, 3, 4) is the focal length of an ith lens unit, ω is the half viewangle at the wide-angle limit and p3c is the refractive power of theimage side surface of said third lens element of the third lens unit,the following is satisfied:
 0. 255<(fw×tanω)/(f1×|f2|)^(1/2) <0.301;

    0.643<fw×|p3c|<0.799;

    0.212<fw/f1<0.232;

    1.081<fw/|f2|<1.205;

    0.434<fw/f3<0.453; and

    0.376<fw/f4<0.421.


5. 5. A video camera using a zoom lens system according to claim
 4. 6.An electronic still camera using a zoom lens system according to claim4.
 7. A zoom lens system comprising from the side of an object which isa subject: a first lens unit having positive refractive power and fixedin relation to an image plane; a second lens unit having negativerefractive power and performing zooming by moving along an optical axis;a third lens unit having positive refractive power which is fixed inrelation to the image plane and performs condensing; and a fourth lensunit having positive refractive power which moves along the optical axisso that the image plane, which varies responding to the movement of saidsecond lens unit and a movement of the object which is the subject, ismaintained in a certain position in relation to a referenceplane,wherein said first lens unit comprises from said object side: afirst lens element of the first lens unit having negative refractivepower, a second lens element of the first lens unit having positiverefractive power; and a meniscus lens element having positive refractivepower and being convex to the object side; wherein said second lens unitcomprises from said object side: a first lens element of the second lensunit having negative refractive power; a second, biconcave lens elementhaving negative refractive power; and a third lens element of the secondlens unit having positive refractive power and being convex to theobject side surface connected to said biconcave lens element, at leastone of the surfaces of said lens elements of said second lens unit beingaspherical, wherein said third lens unit comprises from the object side:a first lens element of the third lens unit having positive refractivepower; a second lens element of the third lens unit having positiverefractive power; and a third lens element of the third lens unit havingnegative refractive power, at least one of the surfaces of said lenselements of said third lens unit being aspherical, wherein said fourthlens unit comprises at least one lens element of the fourth lens unit,at least one of the surfaces of said lens element of said fourth lensunit being aspherical, wherein, in said third lens unit, said first lenselement of the third lens unit is a biconvex lens, said second lenselement of the third lens unit is disposed so as to be convex to theobject side, said third lens element of the third lens unit has itsobject side surface connected to said second lens element of the thirdlens unit and has its image side surface formed to be concave, and theoverall refractive power of said second lens element of the third lensunit and said third lens element of the third lens unit connected toeach other is negative, and wherein, when fw is the focal length of thezoom lens system at a wide-angle limit, fi (i=1, 2, 3, 4) is the focallength of an ith lens unit, ω is the half view angle at the wide-anglelimit and p3c is the refractive power of the image side surface of saidthird lens element of the third lens unit, the following is satisfied:

    0.255<(fw×tanω)/(f1×|f2|).sup.1/2 <0.301;

    0.643<fw×|p3c|<0.799;

    0.212<fw/f1<0.232;

    1.081<fw/|f2|<1.205;

    0.434<fw/f3<0.453; and

    0.376<fw/f4<0.421.


8. A video camera using a zoom lens system according to claim
 7. 9. Anelectronic still camera using a zoom lens system according to claim 7.10. A zoom lens system comprising from the side of an object which is asubject: a first lens unit having positive refractive power and fixed inrelation to an image plane; a second lens unit having negativerefractive power and performing zooming by moving along an optical axis;a third lens unit having positive refractive power which is fixed inrelation to the image plane and performs condensing; and a fourth lensunit having positive refractive power which moves along the optical axisso that the image plane, which varies responding to the movement of saidsecond lens unit and a movement of the object which is the subject, ismaintained in a certain position in relation to a referenceplane,wherein said first lens unit comprises from said object side: afirst lens element of the first lens unit having negative refractivepower; a second lens element of the first lens unit having positiverefractive power; and a meniscus lens element having positive refractivepower and convex to the object side; wherein said second lens unitcomprises from said object side: a first lens element of the second lensunit having negative refractive power; a second, biconcave lens elementhaving negative refractive power; and a third lens element of the secondlens unit having positive refractive power and being convex to theobject side surface connected to said biconcave lens element, at leastone of the surfaces of said lens elements of said second lens unit beingaspherical, wherein said third lens unit comprises from the object side:a first lens element of the third lens unit having positive refractivepower; a second lens element of the third lens unit having positiverefractive power; and a third lens element of the third lens unit havingnegative refractive power, at least one of the surfaces of said lenselements of said third lens unit being aspherical, wherein said fourthlens unit comprises at least one lens element of the fourth lens unit,at least one of the surfaces of said lens element of said fourth lensunit is aspherical, wherein, in said third lens unit, said first lenselement of the third lens unit is a biconvex lens, said second lenselement of the third lens unit is disposed so as to be convex to theobject side, said third lens element of the third lens unit has itsimage side surface formed to be concave, and said first, second andthird lens elements of said third lens unit are disposed with spacestherebetween, and wherein, when fw is the focal length of the zoom lenssystem at a wide-angle limit, fi (i=1, 2, 3, 4) is the focal length ofan ith lens unit, ω is the half view angle at the wide-angle limit andp3c is the refractive power of the image side surface of said third lenselement of the third lens unit, the following is satisfied: 0.255<(fw×tanω)/(f1×|f2|)^(1/2) <0.301;

    0.643<fw×|p3c<0.799;

    0.212<fw/f1<0.232;

    1.081<fw/|f2|<1.205;

    0.434<fw/f3<0.453; and

    0.376<fw/f4<0.421.


11. 11. A video camera using a zoom lens system according to claim 10.12. An electronic still camera using a zoom lens system according toclaim 10.